A novel mooring tether for peak load mitigation: Initial performance and service simulation testing

Thies, Philipp R.; Johanning, Lars; McEvoy, Paul

doi:10.1016/j.ijome.2014.06.001

Cited by 17 publications

(14 citation statements)

References 11 publications

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“…However, the number of data points available is relatively low, and more data would be required in order to gain more confidence in this result. This result could be explained by the fact that the pre-tension in the mooring system is reduced for low tide, which consequently can lead to snatch loads [17]. The mooring system should be carefully designed for low tide conditions, but other tidal ranges have to be investigated during the design process because peak mooring loads also occur for high tide conditions.…”

Section: Discussionmentioning

confidence: 99%

“…The tidal range needs to be accommodated by the mooring system, either by a specific mooring configuration or mooring materials. For example, the mooring tethers discussed by Thies et al [17] can accommodate the tidal range. For the two mooring configurations presented in this paper, the tidal range was accommodated by chains lying on the seabed and lifted for high tide conditions.…”

Section: Discussionmentioning

confidence: 99%

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On Peak Mooring Loads and the Influence of Environmental Conditions for Marine Energy Converters

Harnois¹,

Thies

Johanning

2016

JMSE

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Mooring systems are among the most critical subsystems for floating marine energy converters (MEC). In particular, the occurrence of peak mooring loads on MEC mooring systems must be carefully evaluated in order to ensure a robust and efficient mooring design. This understanding can be gained through long-term field test measurement campaigns, providing mooring and environmental data for a wide range of conditions. This paper draws on mooring tensions and environmental conditions that have been recorded (1) for several months during the demonstration of an MEC device and (2) over a period of 18 months at a mooring test facility. Both systems were installed in a shallow water depth (45 m and 30 m, respectively) using compliant multi-leg catenary mooring systems. A methodology has been developed to detect peak mooring loads and to relate them to the associated sea states for further investigation. Results indicate that peak mooring loads did not occur for the sea states on the external contour line of the measured sea states, but for the sea states inside the scatter diagram. This result is attributed to the short-term variability associated with the maximum mooring load for the given sea state parameters. During the identified sea states, MEC devices may not be in survival mode, and thus, the power takeoff (PTO) and ancillary systems may be prone to damage. In addition, repeated high peak loads will significantly contribute to mooring line fatigue. Consequently, considering sea states inside the scatter diagram during the MEC mooring design potentially yields a more cost-effective mooring system. As such, the presented methodology contributes to the continuous development of specific MEC mooring systems.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

On Peak Mooring Loads and the Influence of Environmental Conditions for Marine Energy Converters

Harnois¹,

Thies

Johanning

2016

JMSE

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“…One of the key engineering issues of the design and installation of floating WECs is to make sufficiently accurate predictions regarding the maintenance, durability, and reliability of the mooring systems, the marine power cables, and the load-bearing components (Thies et al, 2011a;Thies et al, 2011b;Thies et al, 2012;Thies et al, 2014a;Thies et al, 2014b). Traditionally, the wave energy market has employed mooring concepts adopted from the technology in the oil and gas industry, where chains or wire mooring are often used (Gao et al, 2015;Johanning et al, 2006;Thomsen et al, 2015).…”

Section: Mooring Fatigue and Objective Of The Studymentioning

confidence: 99%

A comparison of coupled and de-coupled simulation procedures for the fatigue analysis of wave energy converter mooring lines

et al. 2016

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Newcastle University ePrints -eprint.ncl.ac.uk Yang S, Ringsberg JW, Johnson E, Hu ZQ. A comparison of coupled and decoupled simulation procedures for the fatigue analysis of wave energy converter mooring lines. Ocean Engineering 2016, 117, 332-345. AbstractMooring systems for floating wave energy converters (WECs) must be designed to survive the cyclical loads and motions to which they are subjected as a result of the wave load-WEC interaction and the motions of the WEC in the random elevation of the sea surface. The current study compares simulation procedures for the fatigue analysis of WEC moorings. The objective is to suggest a simulation procedure suitable for an extensive study of the behaviour of WEC systems and thus for the fatigue analysis of mooring lines. A cylindrical, floating WEC with four spread mooring lines is chosen as case study. The dynamics of the WEC system are simulated and analysed using both coupled and de-coupled models in the timedomain. Four types of simulation procedures are compared using commercial software, DNV DeepC, and an in-house solver, MooDy. A systematic fatigue response analysis based on variations of the numerical and physical parameters is conducted. The results are compared with respect to the fatigue damage calculated using the stress-based approach and the rainflow counting method. The simulation procedure using a coupled model is suggested as the preferred numerical method for capturing the interaction between the components of WEC system, which is proven to be crucial for the fatigue damage evaluation of mooring lines.

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“…This type of mooring may be appropriate for non-directional energy converters. Single point mooring allows a WEC to weather-vane [43][44]. There are several sub-types as listed in Table 2 and it is difficult to define which one is the best without considering the WEC type, location, safety, and cost [45][46][47].…”

Section: Grid Connexionmentioning

confidence: 99%

An Up-to-Date Technologies Review and Evaluation of Wave Energy Converters

Titah-Benbouzid¹,

Benbouzid²

2015

IREE

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The potential of electric power generation from marine renewable energy is enormous. Ocean waves are being recognized as a resource to be exploited for the sustainable generation of electrical power. The high load factors resulting from the fluid properties and the predictable resource characteristics make ocean waves particularly attractive for power generation and advantageous when compared to other renewable energies. Regarding this emerging and promising area of research, this paper presents a complete review of wave energy technologies describing, analyzing and fixing many of the concepts behind wave energy conversion. The proposed review will specifically highlights the main wave energy conversion projects around the world at different levels (demonstration stage, in production, and commercialized projects). In particular, mooring will be discussed, as it is a key feature behind massive deployment of wave energy converters. Finally, a discussion will highlight challenges that wave energy converters need to overcome to become commercially competitive in the global energy market.

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A novel mooring tether for peak load mitigation: Initial performance and service simulation testing

Cited by 17 publications

References 11 publications

On Peak Mooring Loads and the Influence of Environmental Conditions for Marine Energy Converters

On Peak Mooring Loads and the Influence of Environmental Conditions for Marine Energy Converters

A comparison of coupled and de-coupled simulation procedures for the fatigue analysis of wave energy converter mooring lines

An Up-to-Date Technologies Review and Evaluation of Wave Energy Converters

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